Chapter 21: The Cardiovascular System: Blood Vessels and Hemodynamics

Describe the structure and function of arteries

Role: Carry blood away from the heart to other organs

Structure: Thick tunica media (consisting of smooth muscle and elastic fibers)

What are two types of arteries?

1. Elastic (conducting) arteries have large diameters and act as a pressure reservoir, propelling blood forward during ventricular relaxation

2. Muscular (distributing) arteries are medium-sized and capable of greater vasoconstriction and vasodilation to adjust flow to specific regions

Describe the structure and function of arterioles

Structure: Abundant microscopic vessels that regulate blood flow into capillary networks

Role: Known as resistance vessels because they control flow by altering their diameter

• Vasoconstriction increases resistance and decrease flow

• Vasodilation increases flow, decreases resistance

Describe the structure and function of capillaries

Structure:

• Smallest vessels (5–10 μm in diameter), forming "U-turns" that connect arterial outflow to venous return

• Termed exchange vessels, their walls consist only of a single layer of endothelial cells and a basement membrane

Role: Enables exchange of nutrients, gases, and wastes between blood and interstitial fluid

Describe the structure and function of venules

Role: Drain capillary blood and begin the return flow toward the heart

Structure:

• Postcapillary venules are porous and significant sites of nutrient exchange and white blood cell emigration

• Muscular venules have thicker walls and serve as reservoirs for large volumes of blood

Describe the structure and function of veins

Role: Convey blood from tissues back to the heart

Structure: They have thinner walls and larger lumens than arteries

• Many, especially in the limbs, contain valves to prevent the backflow of blood

Outline the vessels through which the blood moves in its passage from the heart to the capillaries and back

• Blood moves from the heart through elastic arteries, muscular arteries and arterioles into the capillaries

• It returns through post-capillary venules, muscular venules and veins back to the heart

Discuss the pressures that cause movement of fluids between capillaries and interstitial spaces

Movement between capillaries and interstitial spaces is driven by bulk flow (filtration and reabsorption)

• Bulk flow = Passive process in which large numbers of ions or particles in a fluid move together in the same direction

Compare and contrast: Filtration vs. Reabsorption

Filtration: Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid

• Promoted by:

  • blood hydrostatic pressure (BHP) (~35 mmHg at the arterial end)

  • interstitial fluid osmotic pressure (IFOP) (~1 mmHg)

Reabsorption: Pressure-driven movement from interstitial fluid into blood capillaries

• Promoted by:

  • blood colloid osmotic pressure (BCOP) (~26 mmHg)

  • interstitial fluid hydrostatic pressure (IFHP) (~0 mmHg)

What balances filtration and reabsorption?

Net filtration pressure (NFP) determines whether the volumes of blood and interstitial fluid remain steady OR changes

• Determines the direction:

  • Positive (+10 mmHg) at the arterial end (filtration)

  • Negative (−9 mmHg) at the venous end (reabsorption)

Explain the factors that regulate the volume of blood flow

Total blood flow is cardiac output (CO), determined by heart rate and stroke volume

• Distribution to tissues depends on the pressure difference (higher pressure drives more flow) and vascular resistance (higher resistance reduces flow)

Explain how blood pressure changes throughout the cardiovascular system

BP is highest in the aorta (~110/70 mmHg) and falls progressively as it moves through systemic arteries, arterioles, and capillaries (~16 mmHg at the venous end)

• It continues to drop in venules and veins, reaching 0 mmHg as it enters the right ventricle

Describe the factors that determine mean arterial pressure and systemic vascular resistance

• Mean Arterial Pressure (MAP) is the average arterial pressure, determined by CO and vascular resistance (MAP=CO×R)

• Systemic Vascular Resistance (SVR) is the total opposition to flow, determined by blood vessel lumen size, blood viscosity, and total vessel length

  • Arterioles are the primary regulators of SVR

Describe the relationship between cross-sectional area and velocity of blood flow

Velocity is inversely related to the total cross-sectional area of the vessels

• Flow is slowest in the capillaries (where area is greatest), which facilitates material exchange

Describe how blood pressure is regulated

BP is controlled by interconnected systems:

• Cardiovascular (CV) center: Located in the medulla oblongata, it receives input from the brain (limbic system, hypothalamus) and sensory receptors (proprioceptors, baroreceptors, chemoreceptors). It provides output via the sympathetic and parasympathetic nervous systems.

• Baroreceptor Reflexes: Carotid sinus and aortic reflexes monitor stretch; a fall in BP triggers increased sympathetic stimulation to raise CO and SVR.

• Hormones: The RAA system, epinephrine/norepinephrine, and ADH increase BP, while atrial natriuretic peptide (ANP) decreases it

• Autoregulation: Tissues automatically adjust local flow based on metabolic needs, responding to physical changes (temperature, stretch) and vasodilating chemicals (NO, H+, K+).

Define pulse

The traveling pressure wave created by the alternate expansion and recoil of elastic arteries

Define systolic BP

The highest pressure attained in arteries during ventricular contraction

Define diastolic BP

The lowest arterial pressure during ventricular relaxation

Define pulse pressure

The difference between systolic and diastolic blood pressure, normally about 40 mmHg

Define shock

Shock is a failure of the cardiovascular system to deliver enough O2​ and nutrients to meet the metabolic needs of cells

Describe the four types of shock

1. Hypovolemic: Caused by decreased blood volume (e.g., hemorrhage).

2. Cardiogenic: Caused by poor heart function (e.g., heart attack).

3. Vascular: Caused by inappropriate vasodilation (e.g., severe allergic reaction or bacterial toxins).

4. Obstructive: Caused by the blockage of blood flow (e.g., pulmonary embolism)

Explain how the body’s response to shock is regulated by negative feedback.

The body initiates compensatory systems to restore volume and pressure:

• Activation of the RAA system (conserves salt/water)

• Secretion of ADH (conserves water)

• Activation of the sympathetic ANS (increases HR, contractility, and causes vasoconstriction)

Define systemic circulation and explain its importance

• Systemic circulation includes all vessels carrying oxygenated blood from the left ventricle to capillaries and returning deoxygenated blood to the right atrium.

• It is vital for delivering nutrients/oxygen to all body tissues and removing wastes and heat

Identify the four principal divisions of the aorta

1. Ascending Aorta: The initial segment emerging from the left ventricle.

2. Arch of the Aorta: The continuation of the ascending aorta that loops to the left.

3. Thoracic Aorta: The portion of the aorta that descends through the chest, ending at the diaphragm.

4. Abdominal Aorta: The segment below the diaphragm that descends to the fourth lumbar vertebra

Locate the major arterial branches arising from each division

• Ascending: Coronary arteries.

• Arch: Brachiocephalic trunk, left common carotid, and left subclavian.

• Thoracic: Visceral (pericardial, bronchial, esophageal, mediastinal) and parietal (intercostal, subcostal, phrenic) branches.

• Abdominal: Visceral (celiac trunk, mesenterics, renals, gonadal) and parietal (phrenic, lumbar, sacral) branches

Identify the two primary arterial branches of the ascending aorta

• Right Coronary Artery: Supplies the myocardium of the right atrium and both ventricles.

• Left Coronary Artery: Supplies both ventricles and the left atrium; includes the major "LAD" branch

Identify the three principal arteries that branch from the arch of the aorta.

In order of origination: Brachiocephalic trunk, left common carotid artery, and left subclavian artery

1. Brachiocephalic Trunk: The first and largest branch; divides into the right subclavian and right common carotid.

2. Left Common Carotid Artery: Supplies the left side of the head and neck.

3. Left Subclavian Artery: Distributes blood to the left upper limb

Identify the visceral and parietal branches of the thoracic aorta

• Visceral Branches: Supply organs

  • Includes Pericardial (pericardium), Bronchial (bronchi), Esophageal (esophagus), and Mediastinal (mediastinum tissues) arteries

• Parietal Branches: Supply the body wall.

  • Includes Posterior Intercostal (ribs/muscles), Subcostal (abdominal wall), and Superior Phrenic (diaphragm) arteries

Identify the visceral and parietal branches of the abdominal aorta

• Visceral Branches: Include the Celiac trunk (GI tract/spleen), Superior mesenteric (small intestine/colon), Inferior mesenteric (rectum/colon), Suprarenal (adrenals), Renal (kidneys), and Gonadal (testes/ovaries).

• Parietal Branches: Include the Inferior phrenic (diaphragm), Lumbar (back muscles/vertebrae), and Median sacral (sacrum/coccyx)

Identify the two major branches of the common iliac arteries

1. Internal Iliac Arteries: Primary supply for the pelvic muscle wall, pelvic organs, and external genitals.

2. External Iliac Arteries: Larger branches that follow the pelvic brim and become the femoral arteries in the thigh

Identify the three systemic veins that return deoxygenated blood to the heart.

1. Coronary Sinus: Receives blood from cardiac veins draining the heart myocardium.

2. Superior Vena Cava (SVC): Returns blood from the head, neck, upper limbs, and thorax.

3. Inferior Vena Cava (IVC): Returns blood from the abdomen, pelvis, and lower limbs

Identify the three major veins that drain blood from the head

1. Internal Jugular Veins: Drains the brain, meninges, and bones of the cranium.

2. External Jugular Veins: Drains the scalp, skin, and muscles of the head and neck.

3. Vertebral Veins: Drains the deep neck and cervical vertebrae

Identify the principal veins that drain the upper limbs

• Superficial Veins: Cephalic (lateral arm), Basilic (medial arm), and Median antebrachial (forearm).

• Deep Veins: Radial and Ulnar (forearm), Brachial (arm), and Axillary (armpit)

Identify the principal veins that drain the abdomen and pelvis

Principal veins include the Inferior Vena Cava, which is joined by the Common iliac, Lumbar (abdominal wall), Gonadal (testes/ovaries), Renal (kidneys), Suprarenal (adrenals), Inferior phrenic (diaphragm), and Hepatic (liver) veins

Describe the importance of the hepatic portal system

It directs venous blood from the GI organs and spleen into the liver before it returns to the heart, allowing the liver to process nutrients and detoxify harmful substances

Explain why pulmonary circulation is important

It transports deoxygenated blood to the lungs to unload CO2​ and pick up O2​, returning the oxygenated blood to the heart for systemic distribution

Describe the disorders that affect blood vessels

• Hypertension: Damaging high blood pressure.

• Atherosclerosis: Reduced compliance and stiffening of arterial walls.

• Varicose Veins: Dilated veins caused by leaky valves.

• Edema: Abnormal increase in interstitial fluid volume

• Thrombophlebitis: Inflammation of a vein associated with clot formation